Atmospheric Patterns and Asian Typhoon Landfalls

The Western North Pacific Ocean (WNP) produces more frequent and intense tropical cyclones (TC) than anywhere else in the world, and these storms greatly impact society. This study examines synoptic scale atmospheric patterns and their effects on landfalling typhoons in Japan, Taiwan and Vietnam using composite analysis at upper and mid-levels of the atmosphere, as well as analyzing teleconnection impacts on tropical cyclone frequency, duration and intensity. Examined Best Track data (1946-2010) shows an increased likelihood of Taiwan landfalls earlier in the season, Japan landfalls mid-season, and Vietnam landfalls towards the end of the typhoon season. The formation locations also differed slightly, with storms that eventually made landfall in Japan forming further east than those that hit Taiwan and Vietnam. With knowledge of these spatial and temporal generalizations, in addition to ENSO phase, probabilities of landfall in a specific region can be established. Composite analysis shows the presence of an upper-level anticyclone in each of the three landfall locations. The overall consensus for all three landfall areas is the tendency for tracks to follow the periphery of the upper-level anticyclones toward their respective landfalls. Vector wind composites also supported the findings of the upper-air composites, clearly showing areas of little to no wind shear in the path of the typhoons, indicating a favorable environment for tropical systems. The vector wind analyses also depicted where the dominant steering mechanism was, usually areas of anticyclonic flow surrounding the ridges. Analysis of the spatiotemporal evolution for selected typhoons shows the development of these synoptic features and how they evolve in relation to the typhoon, in particular affecting its intensity. The effect of ENSO and MJO on tropical cyclone frequency and intensity was also investigated using a statistical and quantitative analysis. 83% of TC during El Nino conditions achieved typhoon strength, with 66% of those intensifying even further to 100 knots or greater. In comparison, about 57% of TC reached typhoon strength during La Nina, and 43% of those reached 100 knot winds. Although the total number of cyclones was equal for the selected El Nino and La Nina events, a Poisson regression showed that during El Nino, the number of typhoon days with winds of at least 100 knots increases by a factor of 3.22 over La Nina years, indicating that TC are more likely to intensify during an El Nino. The average per storm shows that there is roughly one extra day of at least 100 knot winds during an El Nino typhoon than a La Nina typhoon. TC activity during an MJO event seemed to be similar with that of La Nina conditions. This research has many broad implications in the fields of atmospheric, oceanic and social sciences. Being able to identify and understand the atmospheric patterns present during certain landfalls gives us the advantage of recognizing those conditions in the future and taking appropriate action. Comprehending the primary steering controls of typhoons on all spatial and temporal scales, along with their behaviors and inner dynamics, is imperative for forecasting improvements and advancement of our knowledge of the tropical climate system and its variability